Fix z-index of YellowBox

Summary:
In Android, components using an elevation > 0 are able to hide the YellowBox. Especially bad when they happen to hide the dismiss button of the inspector.
Closes https://github.com/facebook/react-native/pull/11777

Differential Revision: D4392027

Pulled By: ericvicenti

fbshipit-source-id: 96ab98520cd54b9bb683d984f9990bf0e90b9a37

Libraries/ReactNative/YellowBox.js

@@ -394,11 +394,13 @@ var styles = StyleSheet.create({
     right: 0,
     top: 0,
     bottom: 0,
+    elevation: Number.MAX_VALUE
   },
   inspector: {
     backgroundColor: backgroundColor(0.95),
     flex: 1,
     paddingTop: 5,
+    elevation: Number.MAX_VALUE
   },
   inspectorButtons: {
     flexDirection: 'row',
@@ -448,6 +450,7 @@ var styles = StyleSheet.create({
     left: 0,
     right: 0,
     bottom: 0,
+    elevation: Number.MAX_VALUE
   },
   listRow: {
     position: 'relative',